Have you read the Conan stories? Robert E. Howard went to great lengths to describe women and Conan's attraction to them. Margaret Brundage always read the stories she was illustrating before painting them. In fact, Howard, Seabury Quinn, and other writers would write scenes into their stories that they thought would inspire more Brundage covers, and clearly it worked! According to an article by Robert Weinberg, Brundage was Howard's favorite cover artist, and Howard was Brundage's favorite pulp writer.
However, I'm not a fan of her depiction of Conan as a normal-looking Roman rather than an over-muscled barbarian as he was described. And she left out background detail completely. Yet, her figures are highly stylized and her colors are incredible. I'm a huge Finlay fan, but his women have been described as placid, and I would have to agree. And it's clear that his early Weird Tales work was influenced by Brundage. It seems like your beef is more with Farnsworth Wright, who favored risqué covers and actually requested sexier paintings from Brundage. Unlike the competing Spicy pulps, her women were strong and showed dignity in peril rather than being depicted with sadistic voyeurism, and they never seemed intentionally seductive or in pain in their peril.
Have you looked through all of the Weird Tales covers? Most of them had women-in-peril images long before Brundage showed up! Perhaps Lovecraft was just sore that his works never received a cover by her...